Hundreds of small fish carcasses and a large dead striped bass washed ashore at Lake Merritt on Sunday, Aug. 28, 2022. Credit: Darwin BondGraham

Fish are dying by the tens of thousands in Oakland’s Lake Merritt and other parts of the San Francisco Bay. The massive die-off follows a weeks-long “red tide” event in which a species of marine algae has grown out of control in much of the San Francisco Bay, turning the waters an unusual rusty red color.

Lake Merritt appears to be hard hit by the fish kill. Over the weekend, people started posting images of dying fish and piles of carcasses washed ashore on social media.

“I’ve seen red tide before, but not on this scale,” said James Robinson, the Lake Merritt Institute’s executive director. “It’s heartbreaking to come out here and see all these dead fish. I don’t know the toll this is going to take on the lifecycles of the lake, but it’s going to have an impact, from the birds that eat these fish to next year’s fish spawn.”

Naturalist Damon Tighe, who documents wildlife in Lake Merritt, posted a map on Sunday showing locations around the lake where he estimated more than 10,000 dead fish had washed up, representing more than 10 species.

The die-off is likely associated with a red tide of Heterosigma akashiwo, microscopic algae that have been observed in the Bay in recent weeks, especially around Alameda island. According to the environmental group SF Baykeeper, the algae isn’t considered harmful to humans, but it may emit toxins, and “a bloom of this magnitude has not occurred in the region since 2004.”

The San Francisco Estuary Institute published an advisory on Aug. 26 that fish kills were already being observed in parts of the Bay, including Lake Merritt.

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A rock crab feasting on dead fish at Oakland’s Lake Merritt on Monday, Aug. 29, 2022. Credit: Darwin BondGraham

When The Oaklandside visited Lake Merritt Monday morning, small dead fish were visible around most of the shoreline, and a large number of small and large fish had washed up near the footbridge at the south end of the lake.

There are reports of large fish like sharks, rays, and striped bass washing ashore in San Mateo County, Marin County, and other parts of the Bay, indicating the mass death event is widespread.

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A dead halibut, a predatory fish that can live for decades and grow many feet in length. Credit: Darwin BondGraham

Robinson said he documented thousands of smelt, small fish usually a few inches in length, about 100 striped bass, which can grow several feet in length, and a dozen bat rays among the dead at Lake Merritt as of Monday morning.

At 1 p.m. on Monday, Tighe posted that he’d counted over 522 dead striped bass in the lake’s western arm. Numerous bat rays also appear to have died from the algae bloom over the past 24 hours.

Robinson said tests still need to be done to determine the exact causes of the fish kill, but that local and state environmental authorities are working on it.

This is a developing story. Check back later for updates.

Before joining The Oaklandside as News Editor, Darwin BondGraham was a freelance investigative reporter covering police and prosecutorial misconduct. He has reported on gun violence for The Guardian and was a staff writer for the East Bay Express. He holds a doctorate in sociology from UC Santa Barbara and was the co-recipient of the George Polk Award for local reporting in 2017. He is also the co-author of The Riders Come Out at Night, a book examining the Oakland Police Department's history of corruption and reform.